Step 2.5 Argue with Coinbase about if you're a legitimate owner or not

Step 2.6 Coinbase blocks your account citing "Suspicious activity"

Step 2.7 Sign up to three other exchanges, split the loot across them

Step 5 Argue with the bank about the source of funds

Step 6 Argue with tax agency that you'll fill out your taxes correctly

Kraken would cause no problems for 2.5-2.7

Taxing this is super simple, you just mark as "other" - akin to finding money on the ground.

Arguing with bank - which specific bank would cause problems here?

Even if this is true (and I suspect it's exaggerated), I'd be happy to go through this trivial amount of hassle for $400K.

For something like $10k-20k I bet you could get someone (good lawyer?) to solve those problems for you, leaving you with $399-398k. Worth the deal, I think.

The math doesn't check out

Hence the need for a really good lawyer

Still better than depositing $400K of cash in a US bank.

If you have all of your ducks in a row this is actually much easier than it sounds.